Controller for electric motors



A. T. CROCKER.

CONTROLLER FOR ELECTRIC MOTORS.

APPLICATION msn ocT.28,19|8.

1,352,249. PatentedSept. 7, 1920.

o l L' Y i L B Pis-2 T Inventor:

UNITED STATES PATENT OFFICE.

ARTHUR T. CBOCKEB., oF SCHENEOTADY, NEW vonk, AssIGNOR To GENERAL ELECTRIC COMPANY, A CORPORATION or NEW YORK.

CONTROLLER FOR ELECTRIC MOTORS.

Application filed October 28, 1918.

Be it known that I, n'rirnn T. Cnociinn, a, citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Controllers for Electric Motors, of which the following is a specification.

My invention relates to the control of electric motors and .has for its object the provision of improved means whereby the motor may be started, stopped and generally controlled in a reliable, simple and efficient manner.

My invention relates more specifically to pneumatically operated controllers of the type in which a step-by-step movement is desired. In the pneumatically operated controllers, difficulty has been encountered in securing` a positive and definite stop, there being a tendency to over-travel, which results in trouble at the controller contacts. In the usual type of pneumatic engine, for instance, a piston is moved forward an increment in a cylinder for each step of the controller, and it is difficult to insure that the piston shall move only the predetermined distance, since owing to the inertia of the parts, there is a decided tendency to overtravel.

In order to overcome this difficulty and at the same time provide a pneumatic engine which is very easily controlled, I employ a multiple cylinder engine which I have shown as having three cylinders, 120 degrees apart, provided with a driving member which is acted upon successively by the pistons and so arranged that as each piston reaches the end of its stroke in driving the member forward, the member reacts equally on opposite sides of the line of thrustof the piston, so as to positively stop the Amovement of the member without overtravel.

In one embodiment of my invention the driving member is in the form of a crank provided with two crank pins adapted to be engaged by a Hat' driving snirfacel on each piston. -When the driving surface of a piston in its forward thrust engages only one of the pins it will rotate the crank until the other pin engages the surface, whereupon a balanced condition, in which therev is no turning ,moment on the crank, will exist. This is the end of the stroke and no amount of pressure against the piston or inertia of the parts will give the crank any Specification of Letters Patent.

will drive the crank. Not

Ving upon which of the two remaining PalftontedkSept 7, 1920.

Serial No. 259,902.

tendency whatever to overtravel. Furthermore, in this final position of the piston the two pins, although immovable by the piston which has just operated, are nevertheless in operative relation to the two other pistons, one pin being-engaged by each piston so that a forward movement of either piston only will either of the pistons now drive the crank, but

.either a forward or reverse movement of the driving crank may be obtained dependpistons is operated. At the end of any stroke, therefore, the engine may be reversed by applying air pressure to the piston which operated the previous stroke instead of applying pressure to the next succeeding pis` ton to give a forward movement. In addition to positively stopping the controller at the, end of each step, therefore, my invention constitutes a very convenient arrangement for reversing the movement of the eontroller. Other objects and purposes of my invention will appear in the course of the following specification in which I have shown my invention embodied in concrete form for purposes of illustration.

In the accompanying drawings, Figure 1 is a sectional view of a pneumatic engine through the cylinders embodying my invcntion, and F ig. 2 is a diagrammatic view illustrating the operati-on of the engine.

Referring to the drawings, l is a. controller shaft driven by my pneumatic engine through crank shaft 2 and gearing. This pneumatic enginccomprises three cylinders the center lines of the cylinders being radial to the center line of the shaft, at equal distance from each other, that is, 120 degrees apart. Pistons (i. 7 and 8 fit into the cylinders f3.. et and 5 respectively. and are arranged to drive the crank shaft with a stephy-step movement. a com plete stroke of each pistoncorrespoiuling to an angular movement ot' 120 degrees of the crank shaft. bisch pistou is single acting, that is, it drives in one direction only and is returned freely by the opcratimi of the succeeding piston. Instead of connecting the crank shaft with the pistons in the usual manner by a connecting rod journaled on the crank shaft, the crank is free with respect to the connecting rod. that is, the connecting rod pushes the crank shaft forward but is not attached to it. The arrangement is such that when the piston makes its complete stroke it is positively and accurately stopped. ln this position the movement of one of the other pistons will turn the crank shaft in one d1- `rection, while the movement of the other piston will turn the crank shaft in the opposite direction. y 'l` he particular connection between the pistons and the crank shaft which 'l have illustrated comprises a triangular shaped memberl 9 provided with rollers l() and 1l at two of the corners, while the third corner is secured to the crank shaft 2. rlhe pistons are provided with driving heads l2, 1 3 and lll, each having an elongated shank 15 pivoted to its piston at 16. These rlriving heads slide in guides l'and have flat driving surfaces which engage the rollers 10 and 11.

The operation of my improved positive stop arrangement will he clearly understood from a consideration of Fig. 1. In this ligure, piston has completed a stroke and the two rollers 10 and 11 both engage the flat surface of the driving head 12 at equal distances on opposite sides of the center line of the piston. The piston, therefore, has no turning moment whatever upon the crank shaft, but on the contrary if air pressure is maintained on the piston it has a positive stopping effect depending upon the distance apart of the rollers 10 and 11 and to a certain extent upon the pressure applied to the piston. lt will be further noted from Fig. l that while the crank shaft member 9 is in a position of equilibrium with reference to the driving heads 12, this is not true with reference to the driving heads 13 and 14. The roller 10 on the crank memberv enga-ges the driving head 13 to the left of the center line of thrust, so that any forward movement of this head will drive the crank member, and hence the crank shaft, in a clockwise direction, whereas the roller 11V occupies an opposite position with reference to driving head lll, and hence a forward movement will drive the crank member in the opposite direction, providing pressure is not maintained against piston 6. This same relative position of the parts is assumed at the end of each stroke, so that by supplying pressure to one of the two pistons which are in retracted or operative position, the crank will be turned in one direction, while hy supplying pressure to the other it will be turned in the opposite direction.

ln Fig. 2 l have illustrated diagrammatically a valve arrangement whereby the admission of the air to an exhaust from the cylinders is controlled. Referring to'this drawing it will loe seen that l have provided two electromagnetic valves, which l shall designate as a whole as fr and B respectively. These valves are normally held in an open position by springs a` and o respectively. l have shown thesevvalves only diagrammatically in order to illustrate their function and have not attempted to show their structural arrangement. Each of these valves has two positions, one of which it assumes when its 7inding is energized and the other when it is denergized. Valve B is shown for purposes of illustration and to facilitate an umlerstai'iding of the arrangement as a triple valve, that is, there are three movable members 20, 21 and 22, one for each cylinder, whereas the valve A is shown as having only a single valve member. lf the two valves A and B are both in the same position, air is admitted to a cylinder and the crank shaft will be rotated, Vthe direction depending upon the position of the valves. lf they are both in the energized position, the movement will be forward, whereas if they are both in denergized position the movement will be reversed. is shown in Fig. 2, for instance, the valves are both in energized position and air is admitted-to cylinder 3 so as to give a forward or clockwise rotation, but if the valves were both in denergized position, the cylinder 4l would receive air and the direction of rotation would be reversed. lf, therefore, the two valves were left in either the energized or denergized position, the shaft would continueto rotate in either a forward or reverse direction until it reached a positive stop, whereas if the valve B alone he moved to the opposite position without changing valvey A, or if the two valves occupy opposite positions, the (mei-ation of the engine will be stopped. rfhe arrangement which l employ, however, is such that while valve il is left in one position, whena movement of the controller through more than one step is desired, the valve B is moved to deenergized Vcloseifl position by spring 25, and is opend by the rotation of a `star i teeth corresponding with the steps of the controller' and rotating therewith. As shown, a proie-cation 27 (a roller in Fig. l) engages the teeth of the star wheeland lifts the switch arm to open the circuit of the magnet B at contacts 28. lllhen it is lifted, however, it is held in raised position by a magnet 29 which is energized from the master controller C direct to ground. ln order to take another step, therefore, the magnet 29 mustv be denergized by the op` erator so as to permit the spring 25 to force the switch member to closed position. 'As

wheel 26, having each step Iliade, therefore, the master controller being in position 2, the circuit of the winding ot valve l5 is automatically opened by the star wheel and is closed by the opta-atei' movingr the master controller back to position l, thereby deenergizing magnet 2), and then back to position 2 which rcinergized winding lil. The result is that the controller takes a. step at a time in accordance with the movements ot the master controller by the operator from position 2 to position l and back.

l shall now describe in detail the arrangement of the valves and air passages whereby the result above described is accom plished. For purposes ot illustration l have shown the rotating valve as being composed ot an outer ring or passage 3() eonnccted with a segmental l'iassage 3l. These two passages are shown shaded and re: ei ve air 'from the reservoir through valve A and conduit 32. There is also an inner ring 33 and an outer'segmental ring 34 connected to it, which 1. have shown stippled, this being connefted with the valve by conduit 35. Valve A being in its energized position, therefore, as shown in the drawing, the shaded passages will receive air under pressure from the reservoir, whereas if the valve A is in its upper or deenergized position, the stippled passages will receive air under pressure from the reservoir. Then one passage is connected with the reservoir the other is connected with the exhaust. There is also a segmental passage 3G which l have shown dotted, and which is connected to the exhaust, 'for purposes which will hereinafter appear. lt will be understood, of course, that these circular passages form part of a sliding valve which revolves 12() degrees at a step, that is, l2() degrees upon each complete stroke ot' a piston, and that the conduits connccl'ed with these passages are stationary.

Assume now the parts in the position shown in the drawing, the winding of the valves A and B being energized, air under pressure will enter the conduit 32 through the valve A, thence through the outer passage 3H to the inner passage 3f, conduit 37, to the valve member 2l, Athrough thc conduit 38 to the cylinder Since both of the other cylinders are now connected to exhaust (cylinder l. through conduit 39, valve member 22, conduit 40, through the passage 3G to exha ust 3(5, and cylinder 5 through conduit all, valve member' 20, conduit 42, passages 34 and 33 and conduit 35), the piston G will be forced forward rotating the crank shaft in a clockwise direction as shown in Fig. 2. The piston 8 of cylinder 5 which has just made a stroke is at the limit of its movement and is, therefore, forced backward and the piston '7 of cylinder l is near its inward limit and is forced back slightly. As the piston G nieves torward its tnll stroke, the shaft will be rotated in a Inanner heretofore described. As the shaft moves forward the magnet winding B is deenergized at the contacts 2S and the valve vB moves to its opposite direction, the result of which is to interrupt the pastrom the conduit 37 to conduit :38, and open conduit 3S which is now in engagement with passage 31 to conduit 38, thus maintaining air pressure in cylinder 8. The cylinder is not, however, exhausted, as air pressure remains in the cylinder. lt will be understood, of course, that during this step the sliding valve will revolve 120 degrees so that the end of the passage 3l passes into cooperating engagement with the conduit 4() which, however, is now cut off from cylinder 4 by the valve member 22. If the operator desires to move another step, he moves the master controller back to position l to denergize the winding 29, and then back to position 2, so that the circuit of the winding of valve B will be again conlpleted, thereby leaving the val ves A and B once more in energized position. The pas sage is now open from conduit 41) to cylinder 5L so that the piston 7 moves i'orward and at the same time cylinder 3 is exhausted through the conduit .257 which is now in engagement with passage 34 so' that the exhaust takes Vplace through conduit 35. The result is that the controller moves forward another step. In the same way by moving the master controller to position l and lia-.fk to position 2, the air pressure will be admitted to cylinder 5 through conduit 42, which upon the second step will be in engagement with passage 3l.

Suppose now that instead of going continuously forward the operator wishes to reverse. Assume that the parts are in the position shown in Fig. 2, that is, a stroke has just been completed by the piston 8, but the winding of the valve B has not yet been energized by moving the master controller from position l to position 2, and hence the valve is in the upper position. In other words, the operator has not yet moved the master controller to energize the valve B to move forward, but .instead deenergizes the winding of valve A by master controller to ott position to go backward. The valves and B will now both be in the denergized position whii h is the opposite to that shown in the drawing, so that the air pressure instead of being admitted to cylinder 3 will be admitted to cylinder 4. through conduit 35, passage 33, passage 34, conduit 43, valve member 22 and conduit 39. This will drive the shaft in a counter clockwise direction step-by-step, and will continue to operate automatically in that way it the operator keeps the master controller in the off position. To stop,

nel;

the master controller is moved to position l, and to restore the toi-ward movement the master controller is moved to position 2. ln this way the controller will be moved forward one step at a time in either direction at the will ci? the operator.

lt will be seen that l have provided a pneumatically operated controller in which a positive step-bystep movement is brought about under the control oit the operator, the arrangement being such that there is no possibility of over-travel, while at the saine time being very effective and simple.

While l have described my invention as embodied in concrete form and as operating in a specilic manner in accordance Awith the provisions oit the patent statutes, it should be understood that I doinot limit nay-invention thereto, since various modiiications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth Vin the annexed claims.

`What l claim as new and desire to secure by Letters YPatent of the United States is :M f l. A circuit controller comprising a con trolling member, a plurality oi tluid actu ated reciprocating pistons tor successively rotating the member, and driving connections between Vthe pistons and the controlling member whereby at the end of each piston stroke the controlling member reacts equally 'on opposite sides olf the line of centers of the piston and controlling member to positively stop the controlling member without over-travel.

2. A circuit controllerV comprising a con! trolling member, a plurality 'of {iuid' actuated reciprocating pistonsV for successively rotating the men'iber, and driving connecv tions between the pistons and the controlling member whereby at the endA of each piston stroke the controlling member reacts equally on oppositesides or' the line oit cenl Von opposite sides of Vthe line of centers of the piston and crank shaftto positively stop said shaft without over-travel.

1l. A circuit controller comprising' a controlling member,. a, rotating crank for driving the same, a plurality ci? lluid actuated reciprocating pistons for successivelyV rotating the crank, and.V driving connections betweenV the pistons andthe crank whereby atV the end of each piston stroke the crank. re.-

acts equally on opposite sides or' the lineot centers of the piston and crank to positively stop the crank without overtravel.

5. A circuit controller comprising a controlling member, a rotating crank lor driving the saine having two driving pins one `:tor each direction of rotation, a plurality ing the crank until the other crank pin is similarly engaged.

7. A circuit controller comprising a controlling member, a rotating crank for driving the same having two driving pins one for each direction of rotation, aplurality of iliiid actuated reciprocating pistons and connections whereby the piston under pressure will engage one oit said driving pins and rotate the crank until the said piston engages the other driving pin.

8. A. circuit controller comprising a controlling member, a plurality ot luid actuated reciprocating pistons, eaeh having a Hat driving surface associated therewith, and driving pins tor the controlling member, one oli" which is engaged by each flat surface to rotate the member until another pin engages the surface and positively stops the member. Y

9. A circuit controller comprising a con trolling member, a plurality of fluid actu ated reciprocating pistons each having a flat driving surface associated therewith, a rotating crank provided with two pins in triangular relation with. reference to the axis of the crank, one of which is engaged by each flat surfaceto rotate the crank until the other pin engages the surface and positively stops the crank.

10. A circuit controller comprising a controlling member, three. `fluid actuated radially reciprocating pistons each having a flat driving surface associated therewith, a rotating crank provided with pins in triangular' relation with reference to the axis of the crank, each of which is engaged by the flat surfaceo a piston at the beginning of a stroke and both simultaneously engaged by the flat surface of the piston which is at the end of its stroke.

In Vwitness .whereof have hereunto set my hand this 26th day of October, 1918.

'ARTHUR T. CROCKER, 

